OBJECTIVE To examine the effects of exogenous L- and D-arginine on coronary stenosis vasomotion in relation to stenosis morphology.

DESIGN Intracoronary infusions of normal saline, L- and D-arginine (50 and 150 μmol/min), and glyceryl trinitrate (250 μg bolus) were given in 24 patients with coronary artery disease and stable angina. Coronary stenoses were classified as smooth or complex (irregular borders). The diameter of the coronary stenoses and their adjacent reference segments was measured by computed quantitative angiography.

RESULTS During L-arginine infusion a larger proportion of complex stenoses than smooth stenoses dilated by ⩾ 10% (p < 0.01), and the magnitude of dilatation was greater at the site of complex stenoses (p < 0.05). Irrespective of the type of morphology there was a positive correlation (p < 0.01) between the severity of stenoses and the magnitude of vasodilatation to L-arginine. The response to glyceryl trinitrate was similar in the two groups. No significant change was found in either group in response to D-arginine.

CONCLUSIONS In patients with coronary artery disease, coronary stenoses—particularly those of complex morphology—dilate in response to the administration of L-arginine but not D-arginine. This finding is consistent with partial deficiency of the substrate for nitric oxide synthesis, L-arginine, at the site of complex stenoses.